In PvP it also seems to work in a very weird fashion, as mentioned above.

But I have a question, when is protect now supposed to work even? I mean against which type of attacks? To my knowledge it got changed to intercept with autohits now aswell, aslong as they are still in melee range of the person they want to protect and the attack isn´t an AoE.

Is it even supposed to intercept attacks like Sidecut?

I am sure it should atleast block Power Gradiation or Wazabane, which it currently doesn´t seem to block. Atleast not Metal Aegis or Shine Knight. I didn´t test the player version of Protect yet, since I assume they are the same.

This thread has some more relevant information you can use. Ether Invitation won't be blocked unless the person defending has Claret Call on themself, after the update to Protect a long while back. That's not to say it will work at all, however.